Düsseldorf city has 17,000 or so gas lamps. This German city’s municipal power utility plans to replace about 10,000 of them with a technology that is cheaper to operate but so modern that only a handful of cities have begun to use it: light-emitting diodes (LEDs).
So far, only two dozen experimental LED street lamps have been put up in Dusseldorf. Although LEDs can initially be more expensive, they are a lot more reliable and they can last longer than conventional light bulbs.
But LEDs do have drawbacks. The utility reckons that in terms of the total amount of light produced from a watt of electricity, LEDs still do not match fluorescent or sodium lamps. But that will change in coming years as LEDs improve. Anyway, the light from LEDs can be used more efficiently than that from conventional lamps, from the South Westfalia University of Applied Sciences, which developed the Dusseldorf lamps. “You can direct LED light very well,” he says. So instead of casting light all around—often over places that do not need to be illuminated, each LED is directed much like a spotlight.
– from www.economist.com